All arrays can be adjustable?

["Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>]

    Maybe if we could figure out how to express the various types of arrays
    using set language we wouldn't accidentally invert phrases.  For
    example, I think everybody agrees that simple is a subset of
      (intersect not-adjustable not-fill-pointer not-displaced)
    That's the >only< thing that phrase says.  It can't be inverted,
    conversed, contra-positived, or anything to say that simple arrays are
    not adjustable.  The contra-positive (the only thing provably true) is
    that the UNION of adjustable, fill-pointered or displaced arrays is a
    subset of non-simple arrays. 

Gee, it's been a while since I hacked formal logic in any serious way,
but it seems to be true that if X is a subset of the intersection of A,
B, C, and D, then X is (provably) a subset of A.  I cheated and used
little pictures instead of contrapositives (my religion forbids the use
of contrapositives, even among consenting adults), but I think it's
still true.  Maybe I should go audit a logic course and see what I'm
doing wrong.

-- Scott